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FastHJ.cpp
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FastHJ.cpp
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/* solve the Hamilton-Jacobi equation to smooth a raster field
Persson, PO. Engineering with Computers (2006) 22: 95.
https://doi.org/10.1007/s00366-006-0014-1 kjr, usp, 2019
*/
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <algorithm>
#include <array>
#include <assert.h>
#include <cmath>
#include <fstream>
#include <iostream>
#include <math.h>
#include <stdio.h>
#include <vector>
#include <chrono>
#define EPS 1e-9
// for column major order with 1-based indexing
int sub2ind(const int row, const int col, const int zpos, const int nrows,
const int ncols) {
return (col - 1) * nrows + row +
(zpos - 1) * (nrows * ncols); // trailing -1 is for zero-based indexing
}
//
void ind2sub(const int index, const int nrows, const int ncols, int *i, int *j,
int *k) {
int tmp2;
double tmp = (double)index;
double a = nrows * ncols;
*k = std::ceil(tmp / a);
tmp2 = (int)tmp - (*k - 1) * nrows * ncols;
*j = 1 + std::floor((tmp2 - 1) / nrows);
*i = tmp2 - (*j - 1) * nrows;
assert(*i > 0);
assert(*j > 0);
assert(*k > 0);
}
//
bool IsNegative(int i) { return (i < 0); }
// find indices in linear time where A==value
std::vector<int> findIndices(const std::vector<int> &A, const int value) {
std::vector<int> B;
for (std::size_t i = 0; i < A.size(); i++) {
if (A[i] == value) {
B.push_back(i);
}
}
return B;
}
// solve the Hamilton-Jacobi equation
std::vector<double> limgrad(const std::vector<int> &dims, const double &elen,
const double &dfdx, const int &imax,
const std::vector<double> &ffun) {
assert(dims[0] > 0 && dims[1] > 0 && dims[2] > 0);
std::vector<int> aset(dims[0] * dims[1] * dims[2], -1);
double ftol = *(std::min_element(ffun.begin(), ffun.end())) * std::sqrt(EPS);
std::array<int, 7> npos;
npos.fill(0);
// allocate output
std::vector<double> ffun_s;
ffun_s.resize(ffun.size());
ffun_s = ffun;
int maxSz = dims[0] * dims[1] * dims[2];
for (int iter = 0; iter < imax; iter++) {
//------------------------- find "active" nodes this pass
auto aidx = findIndices(aset, iter - 1);
//------------------------- convergence
if (aidx.empty()) {
std::cout << "INFO: Converged in " << iter << " iterations." << std::endl;
break;
}
for (std::size_t i = 0; i < aidx.size(); i++) {
//----- map triply indexed to singly indexed
int inod = aidx[i] + 1; // add one to match 1-based indexing
//----- calculate the i,j,k position
int ipos, jpos, kpos;
ind2sub(inod, dims[0], dims[1], &ipos, &jpos, &kpos);
// ---- gather indices using 4 (6 in 3d) edge stencil centered on inod
npos[0] = inod;
npos[1] =
sub2ind(ipos, std::min(jpos + 1, dims[1]), kpos, dims[0], dims[1]);
npos[2] = sub2ind(ipos, std::max(jpos - 1, 1), kpos, dims[0], dims[1]);
npos[3] =
sub2ind(std::min(ipos + 1, dims[0]), jpos, kpos, dims[0], dims[1]);
npos[4] = sub2ind(std::max(ipos - 1, 1), jpos, kpos, dims[0], dims[1]);
npos[5] =
sub2ind(ipos, jpos, std::min(kpos + 1, dims[2]), dims[0], dims[1]);
npos[6] = sub2ind(ipos, jpos, std::max(kpos - 1, 1), dims[0], dims[1]);
for (std::size_t u = 0; u < 7; u++)
npos[u]--;
int nod1 = npos[0];
assert(nod1 < ffun_s.size());
assert(nod1 > -1);
for (std::size_t p = 2; p < 7; p++) {
int nod2 = npos[p];
assert(nod2 < ffun_s.size());
assert(nod2 > -1);
//----------------- calc. limits about min.-value
if (ffun_s[nod1] > ffun_s[nod2]) {
double fun1 = ffun_s[nod2] + elen * dfdx;
if (ffun_s[nod1] > fun1 + ftol) {
ffun_s[nod1] = fun1;
aset[nod1] = iter;
}
} else {
double fun2 = ffun_s[nod1] + elen * dfdx;
if (ffun_s[nod2] > fun2 + ftol) {
ffun_s[nod2] = fun2;
aset[nod2] = iter;
}
}
}
}
std::cout << "ITER: " << iter << std::endl;
}
return ffun_s;
}
PYBIND11_MODULE(FastHJ, m) {
m.doc() = "pybind11 module for gradient limiting a scalar field";
m.def("limgrad", &limgrad,
"The function which gradient limits a scalar field reshaped to a vector.");
}
// mex it up for usage in matlab
// first args are inputs, last arg is output
//void mex_function(const std::vector<int> &dims, const double &elen,
// const double &dfdx, const int &imax,
// const std::vector<double> &ffun,
// std::vector<double> &ffun_s) {
//
// // this is how you call the function from matlab
// ffun_s = limgrad(dims, elen, dfdx, imax, ffun);
//}
//#include "mex-it.h"
//
// int main() {
// std::vector<int> dims = {81,41,41};
// double elen = 0.05;
// double dfdx=0.15;
// std::vector<double> ffun;
// std::ifstream meshSizes;
// meshSizes.open("/home/keith/HamJacobi/meshsize.txt");
// double d;
// while (meshSizes >> d) //ifstream does text->double conversion
// ffun.push_back(d); // add to vector
// meshSizes.close();
// std::cout << "read it in" << std::endl;
// int imax=std::sqrt(ffun.size());
// auto begin = std::chrono::steady_clock::now();
// std::vector<double> ffun_s = limgrad( dims, elen, dfdx, imax, ffun);
// auto end = std::chrono::steady_clock::now();
// std::cout << "Method took " <<
// std::chrono::duration_cast<std::chrono::microseconds>(end-begin).count()
// << " microseconds\n";
// std::ofstream myfile;
// myfile.open ("/home/keith/HamJacobi/meshsize_smoothed.txt");
// for(std::size_t i=0; i<ffun_s.size(); i++)
// myfile << ffun_s[i] << std::endl;
// myfile.close();
// return 0;
//}